The present invention relates generally to medical devices, and more particularly to an apparatus for facilitating the implantation of a bioprosthetic replacement heart valve, and associated methodology.
In mammalian animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary valves and have leaflets to control the directional flow of blood through the heart. The valves are each mounted in an annulus that comprises a dense fibrous ring attached either directly or indirectly to the atrial or ventricular muscle fibers. Various surgical techniques may be used to repair a diseased or damaged valve. In a valve replacement operation, the damaged leaflets are excised and the annulus sculpted to receive a replacement valve.
Two primary types of heart valve replacements or prostheses are known. One is a mechanical-type heart valve that uses a ball and cage arrangement or a pivoting mechanical closure to provide unidirectional blood flow. The other is a tissue-type or xe2x80x9cbioprostheticxe2x80x9d valve which is constructed with natural-tissue valve leaflets which function much like a natural human heart valve""s, imitating the natural action of the flexible heart valve leaflets which form commissures to seal against each other to ensure the one-way blood flow. In tissue valves, a whole xenograft valve (e.g., porcine) or a plurality of xenograft leaflets (e.g., bovine pericardium) provide occluding surfaces that are mounted within a surrounding stent structure. In both types of prosthetic valves, a biocompatible cloth-covered sewing or suture ring is provided on the valve body, for the mechanical type of prosthetic valve, or on the inflow end of the stent for the tissue-type of prosthetic valve.
In placing a tissue type prosthetic valve in the mitral position, the commissure posts are on the blind side of the valve and may become entangled with pre-installed sutures, and may damage the annulus or tissue during delivery. The difficulty of the delivery task is compounded if the surgery is through a minimally-invasive access channel, a technique that is becoming more common. The problem of entanglement is termed xe2x80x9csuture looping,xe2x80x9d and means that the suture that is used to attach or mount the valve to the heart tissue is inadvertently wrapped around the inside of one or more of the commissure post tips. If this occurs, the looped suture may damage one of the tissue leaflets when tightly tied down, or at least may interfere with valve operation and prevent maximum coaptation of the valve leaflets, resulting in a deficiency in the prosthetic mitral valve.
Some attempts have been made to overcome these problems in current holders for prosthetic mitral valves. An example of such a holder is U.S. Pat. No. 4,865,600, Carpentier, et al., incorporated herein by reference. Carpentier provides a holder having a constriction mechanism that constricts the commissure posts inwardly prior to implantation. The Carpentier device provides an elongate handle to both hold the valve/valve holder combination during implantation, as well as to cause the commissure posts to constrict inwardly. The valve is connected to the valve holder by the manufacturer using one or more sutures, and the combination shipped and stored as a unit. During the valve replacement procedure, the surgeon connects the handle to the holder and locks a locking nut to hold the commissure posts at a given constricted position. The surgeon then attaches the sewing ring of the valve to the native valve annulus with an array of sutures that has been pre-embedded in the annulus and extended outside the body. The valve is then advanced along the array of sutures to its desired implantation position and the sutures tied off. When the holder is cut free, the commissure posts are released to expand and the holder may be removed using the handle. The inability to remove the elongate handle while maintaining commissure constriction is a detriment. The handle must be attached to the holder so that the commissure posts remain in a constricted position during attachment of the array of sutures to the sewing ring. This can be awkward for manipulation of the valve/valve holder combination during this time-constrained operation. Further, the relatively wide holder periphery may interfere with the attachment step.
What is needed then is an improved tissue-type prosthetic valve holder attachable to the inflow end of the valve that can constrict the commissure posts with or without a handle being attached, yet provides improved visibility and accessibility to the surgeon during the valve attachment steps.
The present invention provides a holder for a tissue-type prosthetic heart valve having an inflow end and an outflow end and a flow axis therebetween. The valve includes an annular suture ring at the inflow end attached to a stent having posts circumferentially-spaced about the flow axis that support occluding tissue surfaces of the valve. In this type of valve the posts are cantilevered generally in the outflow direction.
The holder includes a valve abutment portion sized and shaped to abut the suture ring at the inflow end of the valve. The holder further includes a commissure post constriction mechanism adapted to constrict the commissure posts radially inward from a relaxed position to a constricted position when actuated by a handle adapted to operatively connect to the commissure post constriction mechanism. A retaining mechanism is also provided that retains the commissure post constriction mechanism in the constricted position after the handle is removed.
In one embodiment the commissure post constriction mechanism comprises an adjusting portion and an adjusting member adapted to adjust the distance between the adjusting portion and the valve abutment portion and one or more filaments attached to the adjusting portion and sutured through the end of the commissure posts distal the adjusting portion. When the adjusting member is operated to separate the adjusting portion from the valve abutment portion the adjusting portion pulls the filaments, which in turn urge the end of the commissure posts distal the adjusting portion radially inwardly, to the constricted position.
The valve abutment portion may be of a planar shape, with the adjusting portion of a substantially complementary planar shape to the valve abutment portion. It is preferred that the planar shape of the valve abutment portion be comprised of a plurality of tangs radiating from a central body to each cover a portion of the suture ring. In this manner a sufficient amount of the suture ring is left exposed to allow for suturing the suture ring to the native annulus.
Adjustment of the distance between the valve abutment portion and the adjusting portion may be achieved by providing a central threaded aperture in the adjusting portion and an adjusting member that cooperates with this threaded aperture. In this construction the end of the adjusting member proximal the valve abutment portion abuts the valve abutment portion during operation. When the adjusting member is advanced through the central aperture of the adjusting portion it pushes the valve abutment portion and the two portions separate.
A handle may be operatively connected to the adjusting member to turn it by providing a handle that has an externally threaded end portion and an adjusting member having a central longitudinal threaded bore sized to receive the threaded end of the handle. When the handle is introduced into the bore it is rotated in a first direction and will seat in the threaded bore of the adjusting member. Further rotation of the adjusting member separates the adjusting portion from the valve abutment portion, as recited above, and causes the commissure posts to constrict inwardly.
In the prior art the handle would have to remain attached during suturing of the suture ring to the host tissue to keep the commissure posts in the constricted position. The holder with the handle connected were removed by severing the filament(s). and removing the holder, handle and filaments together.
In accordance with the present invention, the adjusting member itself may be adapted to be the retaining mechanism. Preferably, the adjusting member threads create a greater frictional resistance with the threaded aperture of the adjusting portion than that between the threaded end of the handle and the threaded bore of the adjusting member. This frictional resistance between the adjusting member and the central aperture allows the handle to be further rotated in a second, opposite direction, and the handle will detach or unscrew from the adjusting member without moving the adjusting member, leaving the commissure posts in the constricted position. The tug of the filaments themselves on the adjusting portion when the commissure posts will cause the adjusting member/central aperture thread interface to bind and so may be used to achieve the requisite additional frictional resistance required for allowing the handle to be unscrewed.
In alternative embodiments other mechanisms may be used in accordance with the invention to act as the retaining mechanism. For example, a ratchet assembly may be provided to lock the valve attachment and adjusting portions apart, allowing the handle to be removed while leaving the commissure posts in the constricted position. A ratchet assembly may be comprised of a one or more toothed members affixed to the valve abutment portion that each engage a complementary notch, opening or, for example, a pawl affixed to the adjusting portion. As the valve abutment portion and the adjusting portion are separated by the adjusting member the successive teeth of the toothed member engage the notch, opening or pawl affixed to the adjusting portion, locking the two portions apart.
The present invention further provides a method for retrofitting a holder for a tissue-type prosthetic mitral heart valve attachable to a surgical delivery handle. The heart valve is of the type having an inflow end and an outflow end and a flow axis therebetween, and includes an annular suture ring at the inflow end and radially flexible commissure posts circumferentially-spaced around the outflow end that support occluding tissue surfaces of the valve. The holder has a commissure post constriction mechanism releasably attached to the sewing ring at the inflow end of the valve, the mechanism adapted to constrict the valve commissure posts radially inward from a relaxed position to a constricted position when actuated by the delivery handle. The method includes providing a retaining mechanism that retains the commissure post constriction mechanism in the constricted position after the delivery handle is removed. The retaining mechanism may be provided during the holder assembly process so that the retaining mechanism is attached to and shipped as a unit with the prosthetic valve. Alternatively, the retaining mechanism may be provided separately from the holder and valve combination and the method includes coupling the retaining mechanism to the holder at the time of surgical implantation of the valve. The retaining mechanism and delivery handle may be packaged and sold as a unit. The retaining mechanism desirably comprises an adapter that is interposed between and threadingly engaged to the holder and the handle.
Further in accordance with the invention a method for replacing a heart valve is provided, comprising the steps of removing an existing heart valve to leave an annulus of that heart valve, attaching a holder of the invention to a prosthetic tissue-type heart valve and constricting the commissure posts of the prosthetic heart valve with a handle; inserting the valve through the annulus of the heart valve; removing the handle while leaving the commissure posts in the constricted position; suturing the tissue-type heart valve to the heart annulus, and detaching the holder from the prosthetic heart valve.
After suturing the heart valve to the annulus the surgeon severs the filament, causing the posts of the stent to open to the relaxed, operational position. The severing of the filament(s) also releases the holder from the prosthetic heart valve, allowing it to be removed.
A further understanding of the nature and advantages of the present invention are set forth in the following description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals.